Year	Number of
1990	22.31
1991	22.96
1992	23.46
1993	23.98
1994	24.4
1995	25.04
1996	25.11
1997	24.64
1998	25.21
1999	25.35
2000	24.87
2001	25.31
2002	26.83
2003	28.38
2004	30.09
2005	31.12
2006	32.55
2007	34.2
2008	35.68
2009	37.36
2010	38.85
2011	40.12
2012	41.61
2013	43.05
2014	44.61
2015	46.21
2016	47.64